package sym.qrcode.common.reedsolomon;

import java.util.Vector;

public final class ReedSolomonEncoder {

	private final GF256 field;
	private final Vector cachedGenerators;

	public ReedSolomonEncoder(GF256 field) {
		if (!GF256.QR_CODE_FIELD.equals(field)) {
			throw new IllegalArgumentException(
					"Only QR Code is supported at this time");
		}
		this.field = field;
		this.cachedGenerators = new Vector();
		cachedGenerators.addElement(new GF256Poly(field, new int[] { 1 }));
	}

	private GF256Poly buildGenerator(int degree) {
		if (degree >= cachedGenerators.size()) {
			GF256Poly lastGenerator = (GF256Poly) cachedGenerators
					.elementAt(cachedGenerators.size() - 1);
			for (int d = cachedGenerators.size(); d <= degree; d++) {
				GF256Poly nextGenerator = lastGenerator.multiply(new GF256Poly(
						field, new int[] { 1, field.exp(d - 1) }));
				cachedGenerators.addElement(nextGenerator);
				lastGenerator = nextGenerator;
			}
		}
		return (GF256Poly) cachedGenerators.elementAt(degree);
	}

	public void encode(int[] toEncode, int ecBytes) {
		if (ecBytes == 0) {
			throw new IllegalArgumentException("No error correction bytes");
		}
		int dataBytes = toEncode.length - ecBytes;
		if (dataBytes <= 0) {
			throw new IllegalArgumentException("No data bytes provided");
		}
		GF256Poly generator = buildGenerator(ecBytes);
		int[] infoCoefficients = new int[dataBytes];
		System.arraycopy(toEncode, 0, infoCoefficients, 0, dataBytes);
		GF256Poly info = new GF256Poly(field, infoCoefficients);
		info = info.multiplyByMonomial(ecBytes, 1);
		GF256Poly remainder = info.divide(generator)[1];
		int[] coefficients = remainder.getCoefficients();
		int numZeroCoefficients = ecBytes - coefficients.length;
		for (int i = 0; i < numZeroCoefficients; i++) {
			toEncode[dataBytes + i] = 0;
		}
		System.arraycopy(coefficients, 0, toEncode, dataBytes
				+ numZeroCoefficients, coefficients.length);
	}

}
